Multifrequency transmission measuring system



June 13, lw33.y I v vA.A L. lMATTE MULTIFREQUNCY TRANSMISSION MEASURING SYSTEM 3 sheets-sheet `1 Filed Deo.

@SWW @mwa BARN @LM/afk A. l.. MATTE Filed Dec. 1B, 1950 3 Sheets-Sheet 2 June 13, 1933. A, L. MATTE MULTIFREQUENCY TRANSMISSION MEASURING SYSTEM 3 Sheets-Sheet 3 Filed Deo.

er Ch ff/Nature INVENTOR HZ. .Milde BY TToRNEY Patented June 13, 1933 Uurr-nn'sinfri-:s-

orifice i ANDREW LMATTE, or SUMMIT', :NEW :mesma Assrefivon 'ro AMnnrcAN TELEPHONE AND TELnGRArn COMPANY; A oonronnirron 'for Nnvv` YORK applicati@ nieu neuem-beiy1e, issu. .serial no. maanr rlhis inventionA relates to a systemfor `determining .theY transmission efficiency @of 4a circuit, and particular-ly to a ysystem in which the .transmission'ei'iciency is measured lat 5 each .of a plurality of frequencies, which frequencies are transmitted.simultaneously over the said circuit.

in a linear circuit such asanpattenuator composed of resistances only, electrically re- El@ mote from inductive-or other-disturbing cur-l rents, .the `transmission measurements mad-e at a single frequency., which frequency 1s the only one present in the system, would v,be the' same as the measurements made at lasingle L? frequency during the presence of 'other frequencies` vin thesystem.A :Su-chy .equality .does not exist in the case of long'transmission lines, particularly where relatively energy levels are used, since kcrowding andmodulation take place. Those phenomenagive rise current received to the 1,000-.cycleY currentv transmitted, but the ratio of the of all of the frequencies received `to Vthe, 1,000-.cycle current transmitted. The error created rby the parasitic frequencies `4can be eliminated by using a filter that cuts off all frequencies above about 1,000 cycles. Y

When a number of frequencies aretrans-` mitted simultaneously through 1a non-linear network, such as a transmission line, there are in addition to the harmonics resulting from the crowding at each frequency, new com-bi- 1 nation frequencies, all of which exact their toll of energy from that of the impressed 'currents. If selective. networks are used at the receiving end and care is taken that noneof the impressed frequencies lead to modulation products that fall within the free transmit- Cfu tingbands of the receiving filters, the loss suffered by .each .transmitted frequency can be measured by itself and the .effects of modulation VinV increasing .line losses may .be Idetermined. Conversely, by yselecting' suitable transmitted*frequencies the modulation products can be measured by vsuch .a Adevice by having them frail within 'the free transmitting range of one of the receiving filters.

This inventioniresi'des, in part, in a method :that consists `essentially in causing a current .to `flow over the circuit whose transmission eiliciency is to be measured, which current comprises :a number of ,frequencies Whose magnitudes are fixed, separating the current of, each frequency .at the receiving end by mea-ns of `selective networks, then measuring the VYcurrent .of .each frequency, and determining its ratio to the transmitted current. Other objects of this invention will be apparent from the following description when read connection with the lattached `drawings, of which igure l shows a form of embodiment Yof the invention in which visual indi-cations of the transmission .efficiency at 75 each .of the receivedfrequencies are successively given.; Fig. 2 shows an alternative form of indicator, Adesignated a Visualizer, that renders possible the observation of the indications .of the transmission equivalent of the .circuit `atall of the frequencies simultaneously; FigsB and y3a represent a plan and a cross-section of a modification-of Fig. 1 to permit the making of a record on a printed form after the transmission equivalent has been visually observedat a measuring frequency; and F ig. 4represents a form 'of chart to be used in connection with the arrangement shown in Fig. .3.

D Fig. l represents the application 'of the 90 invention to an .arrangement i-n which the transmission .equivalent is indicated by suitable apparatus at three frequencies, but it will be understood that a greater -or smallery number of frequencies may be used. In Fig. l, G1, G2 and G3 represent sources of current of each of three frequencies that are intended to transmitted simultaneously over the circuit fto be tested. Each Y-of the generators 1s connected to the primary winding of one 10 of the transformers T1, T2 and T3, across the secondary windings of which are connected the potentiometers P1, P2 and P3, respectively. Those potentiometers are connected with the contacts of the switches S1, S2 and S3, and with each other, so that one or more of the generators may be effectively connected with the grid circuit of the vacuum tube V1 that acts as a voltage integrator. The output of the said tube is connected by the transformer T2 with the movable arms of the switch S2. Bridged across the circuit between transformer T2 and switch Si is a Calibrating circuit that includes a band pass filter F1 that is intended to pass one of the Jfrequencies lying within the range represented by the generators G1, G2 and G2. The filter is connected with a potentiometer P1 that controls the amplitude of the voltage applied to the calibrating detector D1', the output of which is connected with the winding l of the differential galvanometer DG1. While this calibrating current is shown as derived from one of the measuring sources for convenience, it will be evident that it might be obtained from any other steady source suitable for causing the desired deflection of the galvanometer DS1.

The outer contacts of the switch S1 are connected through the jacks J1-J1 and the as- Y sociated cords to the circuit to be tested, designated as L1. The inner contacts of the switch S1 are connected to the thermocouple TG1 which, in turn, is connected to the milliammeter A1. The circuit L1 is connected through the jacks J 2-J 2 and their cords to the amplifier BA1. The output circuit of that amplifier is branched and each branch contains one of the selective networks F1, P2 and P3. Connected to the output of each of those networks is one of the potentiometers P5, P6 and P2. The switches S5, Ss and S2, which are associated with those potentiometers, are adapted to connect them with the input of the line detector D2 (which has a high input impedance), the output of which is connected with winding 2 of the differential galvanometer DGr2.

The east station comprises also transmitting apparatus similar to that heretofore deacks Jef-J2 and the associated cords to the circuit L2, which in turn is connected through the jacks J1J.1 to receiving apparatus similar to that previously described in connection with the east station. The same numbers primed have been used to indicate the receiving apparatus at the west station corresponding to that at the east station.

Prior to the making of transmission measurements the apparatus must be calibrated. To do so i't is necessary to adjust the magni tude of the transmitted currents at each test frequency. Accordingly the switch S1 is operated so that the ammeter A1 will be effectively connected with the output of the tube V1. With key S1 operated downwardly, and S2 and S3 in their upper positions, the output of generator G1 only will be connected with the tube V1. The potentiometer P1 is then adjusted until the desired magnitude of current is indicated by A1. Then S1 is moved to its upper contact and S2 to its lower contact, thereby connecting G2only to the input of V1. The potentiometer P2 is then adjusted until the desired current is indicated by A1. In like manner, the adjustment of 'the potentiometer P3 is made to give thev desired current for G2. After such adjustment has been made, all of the switches S1, S2 and S2 are thrown to 'their lower positions, thereby connecting all of the generators in combination with the input of the tube V1. The current of one of those frequencies will pass through the filter F1, and will be rectified by the detector Dl, and the resultant rectified current will flow through vthe winding l of the differential galvanometer. The potentiometer P.1 is then set at its mid position and tie deflection of the needle of the galvanometer is noted, and called the zero position. Y

After that adjustment has been made the plug 4 of the cord 5 should be inserted in the jacks J1 and the plug 6 in the jacks J1. Then the switch S4 is operated outwardly and the output of the tube V 1 will be transmitted over the cord 5 and impressed upon the amplilier BA1. The ouput of that amplifier will be impressed upon 'the branches containing the filters F1', F2 and FJ, each of which is adapted to select one of the-frequencies produced by the generators, and to impress it across one of the potentiometers P5, PG and P7. Each potentiometer has a switch associated therewith by which the voltage at the selected frequency may be impressed upon the line detector D2 which has a high input impedance. lt is desirable to point out that the impedance of the thermocouple TG1 is the same as that ofthe line L1, adapted to be connected with the switch S4, and also the same as that of the amplifier BA1', so that the disconnection of the thermocouple and the connection of either the line L1 or the amplifier BA1 does not alter the output impedance of the tube V1. With the output of that tube connected by the cord 5 to the said amplier, each of the frequencies is in turn selected by the manipulation of the switches 55', 52 and 57', and the voltage is impressed upon the detector D2. Considering for example, the frequency passed by the filter F1, the switch S5 is closed and the potentiometer P2 is adjusted until the current that flows through the winding 2 is suiicient to cause 'the needle of the differential galvanometer DS1 to be restored to its Zero position. In like manner,

the potentiometers P6 fand P7 are adjusted for `the currents Yof their respective frequencies. Similar calibration must Abe niade at the .east ystation before it can be used for straightaway measurements.` n

With the `.potenticmeters thus adjusted, the plugs 4 and 6 `,are withdrawn from their respective jacks, and the amplifier BA1 is connected totheline 1L2 vwhich in turn-is connected to the source of current at the .east station, yiz the `vacuum 'tube V1 and the generators G1', GL" and G3" associated therewith, which source 7has been calibrated the manner described '.above.V The system then 4is arranged -to measure the-transmission efficiency of the :circuit L2. To do this the switch S is closed, thereby selecting one of the frequencies transmitted from the Yeast station over the line L2 to the west station. T he potentiometer P4 is then varied andthe transmission efficiency ofthe system aboye or below a zero loss wil-l be -indicated bythe setting yof the potentiometer .13.4. In like manner, the transmission .efficiency of the' frequencies over Ythe same circuit. The are rangement shown in Fig. 2 .di-fiers from .that in Fig. 1 in that it permits the simultaneous observation of the transmission equivalent of the circuitat all measuring frequencies.

' At .the west station of Fig. 2 there is show-n an.alternative,arrangement in which a plurality of generators produce currents .of equal, definite magnitudes, ybut of separate frequency as in Fig. 1,.but .differing from the latter in that each generator is connected to the vcircuit L1 by va separate selectivenetwork. The lline L1 is connected .at theeast station -to a receiving-circuit ,that includes an adjustable potentiometer PS and a receiving .amplifier RAZ. The output of `the amipl-ifier :is .connected to a plurality of branch circuits each including onezof the selective networks F5, F6 and F7, one ofthe potentiometers P9, P and Pn, one of the rectifiers 138 D4 and D5 and one of the indicating `devices A2, A3 and A4, the latter being :preferably .edgew'ise milliammeters. The east station is also equipped with generators, selective networks, and other apparatus corresponding to .those shown at the west station and designated by the saine numbers primed, for transmission over the circuits to the west station; and in like smanlner, the weststation is equipped with receive ing apparatus similar to that shown at :the ea-st station, and indicated by the same numbers primed. I y p A-In order to calibrate the system, the generator equipment at the east station, for example, would be connected by a patching cord similar to5 of Fig. 1 to the potentiometer PS, i. e. the drop side of L1 would be patched to the drop side of L2, not bridged on; and the received energy would be adjusted by the potentiometer to any desired level. The amplifier RAZ, and the potentiometers 139,131@ and P11; would be -radjusted in succession so that the several ammeters would stand attheir midscale i. e. zero positions. Then the local source of vcurrent would be disconnected from the potentiometer P8 and the generators at `the West station whichlhave outputs ofthe same magnitude and frequency as that .at the east station are-connected with the .line Ll which,

` in turn, is connected across the potentiometer P8. The frequencies'transmitted will be seyerally selected `by the networks F5., F 6 and F7, and the resultant rectified currents will .flow through the said ammeters. The .pointers of those instruments will .take positions .corresp ending to the current magnitudes, and thus will effectively plot in space .a transmissionfrequency curve. If rvdesired the .potentiometer P8 maybe `adjusted to .bring back to zero the pointer on ithe milliammeter corresponding to some reference frequency, whereupon .the meters will indicate the departure of the .transmission losses from thatreference frequency. f

e Tfhe arrangement, of which .several views are shown in Figs. 3 and 3a.,.is intended for use in connection with the circuit` of Fig. 1.,

and is designed to make arecord of the transmission equivalent of the .circuit .after .such equivalent has been indicated bythe .apparatus shown Yin the llatter figure. The potentiometer P4, shown in Fig. 1, which ,preferably .is of the slide-wire type, has connected with vits shaft, .as shown in F ig; 3, apinion 10 that meshes with .a rack l1 that is 'connected with .and forms -a part of the .frameworlrfor the support of a chart 12, upon which the record of .the transmission measurement is made.` VAs shown in Fig. 3a, the chart is capable of being moved longitudinally through a .guide 18 of the punch block 14 that contains .a plurality of pins for punching holes in the chart. The number of vpins depends upon the number of test frequencies, -there being one pin for each frequency. To .prevent the operation of any pin other than that corresponding to the frequency under measurement atafparticular time, the arrangement shown in Fig. 3a is provided. The hamnier 15, which is rotated yby thel action of the armature 16 of the magnets 17 of Fig. 3 Whenever the key 18 is closed, does notinove sufficiently to makedirect'conta'ct with the lower ends of the pins of the punch block. To effect the operation of the pins by the hammer, it is necessary to interpose between the hammer and the pin a device such as the finger 18, shown in 8a. As will be seen, tl finger' is controlled by the movement of the key S5 whenever the latter' is thrown in a counterclockwise direction. rihat will cause the end of the finger 18 to move to the left and thus insert itself between the h animer and the pin. It is to be understood, of course, that corresponding fingers and linking means are provided for cach cf the switches SG, S7, ctc., that connect the potentiometers of the receiving circuit of Fig. 1 with the input of the line detector D2.

The method of making a record by the mechanism just described is as follows: Let it be assumed that the frequency that passes through the filter F1 is being measured, the switch S5 would be operated, and the finger 18 will be moved so as to be beneath the lower end of the pin that, in Fig. 3, is horizontally opposite the switch designated After the potentiometer P4 has been adjusted to restore the needle of the differential galvanometer DG2 to its Zero position, the carriage that holds the chart 12 will occupy a certain position with respect to the line of the pins of tile said punch block. As soon as the adjustment of the potentiometer brings the needle to its Zero position, key 18 will be operated, which will energize its magnets and attract its armature 16. That action rotates the shaft 19 and causes the hammer 15 to strike the finger 18. The pin is forced upward, and the paper of the chart will be perforated. rllhe opening of key 18 releases the armature 16 and allows the hammer to drop back. Key S5 is then restored to its normal vertical position and key S6 would be operated, thereby bringing a `finger similar to 18 under the pin that is associated with the latter key.

The chart shown in Fig. 4 illustrates a measurement that is made at twelve different frequencies, but any number of frequencies may be employed, as desired. As shown on the drawings, the chart is in position to be inserted in the chart holder of Fig. 3.

It is, of course, to be understood that the arrangements shown in the figures and described hereinbefore are merely schematic embodiments of the invention for the purpose of illustrating` in simple fashion the manner in. which the invention may be employed. However, the invention is not limited to the forms shown but is capable of embodiment in other and different forms without departing from the spirit and scope of the appended claims.

What is claimed is:

1. In a system for determining the transmission efiiciency of a circuit, the combination with a circuit, of a source of current of a plurality of frequencies connected with the said circuit for simultaneous transmission thereover, means connected with the said circuit to separately select .each frequency, means to rectify the selected frequencies, and an electromagnetic device to diderently compare the rectified current with another current of known value whereby the transmission efficiency of the circuit may be determined.

2. In a system for determining the transmission efficiency of a circuit, the combination with a circuit, of a source of current of a plurality of frequencies connected therewith, a receiving system comprising an amplifier, a plurality of branch circuits connected with the output of the said amplifier, each containing a network selective of'a particular frequency, a potentiometer of comparatively low impedance, and a switch, a rectifier, whose impedance is relatively high compared with that of the potentiometer, adapted to be connected by each switch with each branch circuit, a differential galvanometer having one winding connected with said rectier and the other winding connected with a source of current variable at will.

3. lfn a system for determining the transmission 4efficiency of a circuit, the combination with a transmission circuit of a source of current of a plurality of frequencies connected therewith, and a receiving circuit also connected with the same transmission circuit comprising mea-ns to select each of the frequencies impressed by the said source upon the said transmission circuit, a rectifier for the currents of the selected frequencies, another source of current of a plurality of frequencies, means to select one of the frequencies of said other source, a potentiometer upon which the last mentioned selected frequency is impressed, a rectifier of comparatively high impedance connected with the said potentiometer and an electromagnetic responsive device having dierential windings, each of which is connected with one of the said rectifiers.

4f. In a system for determining the transmission efficiency of a circuit, the combination with a transmission circuit of a source of current of a plurality of frequencies connected therewith, and a receiving circuit also connected with the same transmission circuit comprising means to select each of the frequencies impressed by the said source upon the same transmission circuit, a rectifier connected with all of said selecting means, the connection including a switch individual to and connected with each of said selecting means, another source of currents whose frequencies are the same as those of the said first source, a rectifier connected with the said other source of currents, the connection including a potentiometer, means lso connected with the said other source to select at will one or moreof the frequencies generated thereby, and an electromagnetic responsive device having differential windings, each of Vwhich is connected with one of the said rectifiers.

5. In a system for determining the transmission eciency of a circuit, the combination with a plurality of sources of current of different frequencies, of means to set the current of each frequency at a desired value, a four terminal network upon which all of the said currents are impressed, a receiving circuit comprising means to select each of the frequencies transmitted over the said line, a dierential galvanometer calibrated for known values of received current, means to connect each of the selecting means to the said transmission equivalent of the said line circuit at the measuring frequencies employed.

6. The method of determining the trans mission eiiiciency of a circuit which consists in transmitting simultaneously over a circuit a current of a plurality of frequencies', and indicating the simultaneous magnitudes of the transmission efiiciency of the system at any instant for every frequency employed.

7. The method of determining the transmission efiiciency of a circuit which consists in transmitting simultaneously over a circuit a current of a plurality of frequencies, selecting each of the frequencies employed, separately rectifying the current of each selected frequency, and indicating the simultaneous magnitudes of the currents ofA all frequencies in terms of the transmission elficiency ofthe system at any instant.

8. The method of determining the transmission eiiciency of a circuit, which consists in transmitting over the said circuit a currentcomprising a plurality of components, each of fixed magnitude and of a separate, discrete frequency, receiving the transmitted current and separating by frequency selection the components of said current, measuring simultaneously the magnitudes of the components of all frequencies and indicating the ratio of each component to the component of same frequency as transmitted.

9. In a system for determining the transmission eificiency of a circuit, the combina- 4tion with a circuit over which is transmitted of said amplifier, each branch circuit containing a selective network, a rectifier and a visual indicating device connected with the output of said rectifier.

10. In a system for determining the magnitude of the components constituting the several frequencies of a multifrequency current, the combination with a source of multifrequency currents, of a plurality of branches connected thereto, each branch containing a frequency selective network, a rectifier, and an edgewise indicating milliammeter', the milliammeters of the several branches being arranged side by side. Y i

11. In a system for recording the transmission efficiency as measured by the system of claim 3, the combination with a gear connected with the shaft of the slide wire potentiometer, of a carriage for supporting a paper chart, the said carriage having a rack coa-cting with the said gear, a guide through which the said chart is adapted to pass when mounted upon the said carriage, a plurality of pins mounted beneath said guide, a plurality of fingers, each adapted to be moved beneath one of said pins by the switch of a receiving branch circuit of claim 3, and means operable at will, to cause one of said pins to perforate the chart whenever the finger associated with that pin is in position beneath it.

V12. In a system for recordingrthe transmission eiiiciency of a circuit, the combination with a chart of a pluralityvof perforating devices, each individual to a particular frequency, means to adjust the position of said chart relative to the said perforating devices, and mea-ns, operable at will to cause each of said devices to perforate the said chart to record the transmission efficiency for each of said frequencies. Y

In testimony whereof, I have signed my name to this specification this 17th day of December, 1930.

ANDREW L. MATTE. 

